Flow Analysis

1
Flow Analysis

• Factors that Affect the Flow Pattern
• Flow Analysis Information
• Flow Patterns
• a. Flow within Workstations b. Flow within
  Departments
• c. Flow between Departments
• Flow Planning
• Measuring Flow
• Types of Layout
• a. Fixed Location b. Product
• c. Group Technology d. Process
• e. Hybrid
• Flow Dominance Measure
• Techniques for Machine Cell Formation
• a. Row and Column Masking Algorithm
• b. Single Linkage Clustering c. Average Linkage
  clustering

2
Factors that Affect the Flow Pattern

• Number of parts in each product
• Number of operations on each part
• Sequence of operations in each part
• Number of subassemblies
• Number of units to be produced
• Product versus process type layout
• Desired flexibility
• Locations of service areas
• The building
• . . . .

3
Flow Analysis Information

• Assembly Chart
• Operations Process Chart
• Flow Process Chart
• Multi-Product Process Chart
• Flow Diagram
• From-To Chart

4
Assembly Chart It is an analog model of the
assembly process. Circles with a single link
denote basic components, circles with several
links denote assembly operations/subassemblies,
and squares represent inspection operations. The
easiest method to constructing an assembly chart
is to begin with the original product and to
trace the product disassembly back to its basic
components.
5
Operations Process Chart By superimposing the
route sheets and the assembly chart, a chart
results that gives an overview of the flow within
the facility. This chart is operations process
chart.
6
Flow Process Chart This chart uses circles for
operations, arrows for transports, squares for
inspections, triangles for storage, and the
letter D for delays. Vertical lines connect these
symbols in the sequence they are performed.
7
Multi-Product Process Chart This chart is a flow
process chart containing several products.
8
Flow Diagram It depicts the probable movement of
materials in the floor plant. The movement is
represented by a line in the plant drawing.
9
From-To Chart This chart is a matrix that
contains numbers representing a measure (units,
unit loads, etc.) of the material flow between
machines, departments, buildings, etc.
10
Flow Patterns Flow within Workstations

• Motion studies and ergonomics considerations are
  important in establishing the flow within
  workstations. Flow within workstations should
  be
• Simultaneous coordinated use of hands, arms and
  feet.
• Symmetrical coordination of movements about the
  center of the body.
• Natural movements are continuous, curved, and
  make use of momentum.
• Rhythmical and Habitual flow allows a
  methodological and automatic sequence of
  activities. It should reduce mental, eye and
  muscle fatigue, and strain.

11
Flow Patterns Flow within Departments

• The flow pattern within departments depends on
  the type of department.
• In a product and/or product family department,
  the flow follows the product flow.

2 machines/operator
1 machine/operator
1 machine/operator
END-TO-END
BACK-TO-BACK
FRONT-TO-FRONT
More than 2 machines /operator
1 machine/operator
CIRCULAR
ODD-ANGLE
12
Flow Pat. Flow within Departments (cont.)

• In a process department, little flow should occur
  between workstations within departments. Flow
  occurs between workstations and isles.

Uncommon
DIAGONAL
PARALLEL
PERPENDICULAR
Dependent on interactions among workstations
available space size of materials
13
Flow Pat. Flow between Departments

• Flow between departments is a criterion often
  used to evaluate flow within a facility.
• Flow typically is a combination of the basic
  horizontal flow patterns shown below. An
  important consideration in combining the flow
  patterns is the location of the entrance
  (receiving department) and exit (shipping
  department).

Similar to straight. It is not as long.
L flow
Simplest. Separate receiving/shipping crews
Straight
Very popular. Combine receiving /shipping.
Simple to administer
Circular flow
U flow
Terminate flow. Near point of origin
Serpentine
When line is too long
S flow
14
Flow within a facility considering the locations
of entrance and exit
At the same location
On adjacent sides
15
Flow within a facility considering the locations
of entrance and exit (cont.)
On the same side but at opposite ends
On opposite sides
16
Vertical Flow Pattern
Flow between buildings exists and the connection
between buildings is elevated
Ground level ingress (entry) and egress (exit)
occur on the same side of the building
Ground level ingress (entry) and egress (exit)
are required
Some bucket and belt conveyors and escalators
result in inclined flow
Travel between floors occurs on the same side of
the building
Backtracking occurs due to the return to the top
floor
17
Flow Planning

• Planning effective flow involves combining the
  above patterns with adequate isles to obtain
  progressive movements from origin to destination.
• An effective flow can be achieved by maximizing
  directed flow paths, reducing flow, and
  minimizing the costs of flow.
• A directed flow path is an uninterrupted flow
  path progressing directly from origin to
  destination the figure below illustrates the
  congestion and undesirable intersections that may
  occur when flow paths are interrupted.

Uninterrupted flow paths
Interrupted flow paths
18
Flow Planning (cont.)

• The reduction of flow can be achieved by work
  simplification including
• 1. Eliminating flow by planning for the delivery
  of materials, information, or people directly to
  the point of ultimate use and eliminate
  intermediate steps.
• 2. Minimizing multiple flows by planning for the
  flow between two consecutive points of use to
  take place in as few movements as possible.
• 3. Combining flows and operations whenever
  possible by planning for the movement of
  materials, information, or people to be combined
  with a processing step.
• Minimizing the cost of flow can be achieved as
  follows
• 1. Reduction of manual handling by minimizing
  walking, manual travel distances, and motions.
• 2. Elimination of manual handling by mechanizing
  or automating flow.

19
Measuring Flow

• 1. Flow among departments is one of the most
  important factors in the arrangement of
  departments within a facility.
• 2. Flows may be specified in a quantitative
  manner or a qualitative manner. Quantitative
  measures may include pieces per hour, moves per
  day, pounds per week. Qualitative measures may
  range from an absolute necessity that two
  departments show be close to each other to a
  preference that two departments not being close
  to each other.
• 3. In facilities having large volumes of
  materials, information, a number of people moving
  between departments, a quantitative measure of
  flow will typically be the basis for the
  arrangement of departments. On the contrary, in
  facilities having very little actual movement of
  materials, information, and people flowing
  between departments, but having significant
  communication and organizational interrelation, a
  qualitative measure of flow will typically serve
  as the basis for the arrangement of departments.
• 4. Most often, a facility will have a need for
  both quantitative and qualitative measures of
  flow and both measures should be used.
• 5. Quantitative flow measure From-to Chart
• Qualitative flow measure Relationship (REL)
  Chart

20
Quantitative Flow Measurement

• A From-to Chart is constructed as follows
• 1. List all departments down the row and across
  the column following the overall flow pattern.
• 2. Establish a measure of flow for the facility
  that accurately indicates equivalent flow
  volumes. If the items moved are equivalent with
  respect to ease of movement, the number of trips
  may be recorded in the from-to chart. If the
  items moved vary in size, weight, value, risk of
  damage, shape, and so on, then equivalent items
  may be established so that the quantities
  recorded in the from-to chart represent the
  proper relationships among the volumes of
  movement.
• 3. Based on the flow paths for the items to be
  moved and the established measure of flow, record
  the flow volumes in the from-to chart.

21
Example 1
From-to Chart
Revised Flow Pattern
Original Flow Pattern
22
Flow Patterns
Press
Turning
Store
Milling
Press
Plate
Assembly
Warehouse
Stores Turning
Milling Warehouse Assembly Plate
U-shaped flow
Straight-line flow
Stores Press Plate
Assembly Turning
Milling Warehouse
Stores Milling
Warehouse Turning Press
Plate Assembly
W-shaped flow
S-shaped flow
23
Flow Patterns (cont.)
Press
Turning
Store
Milling
Press
Plate
Assembly
Warehouse
Stores Turning
Milling Warehouse Assembly Plate
U-shaped flow
Straight-line flow
Stores Press Plate
Assembly Turning
Milling Warehouse
Stores Milling
Warehouse Turning Press
Plate Assembly
W-shaped flow
S-shaped flow
24
Qualitative Flow Measurement

• A Relationship (REL) Chart is constructed as
  follows
• 1. List all departments on the relationship
  chart.
• 2. Conduct interviews of surveys with persons
  from each department listed on the relationship
  chart and with the management responsible for all
  departments.
• 3. Define the criteria for assigning closeness
  relationships and itemize and record the criteria
  as the reasons for relationship values on the
  relationship chart.
• 4. Establish the relationship value and the
  reason for the value for all pairs of
  departments.
• 5. Allow everyone having input to the
  development of the relationship chart to have an
  opportunity to evaluate and discuss changes in
  the chart.

25
Relationship Chart
26
Types of Layout
Volume High Medium Low
Product Planning Department
Product Layout
Product Family Planning Department
Fixed Location Layout
Process Layout
Group Technology Layout
Fixed Materials Location Planning Department
Process Planning Department
Low Medium High Variety
27
Fixed Product Layout
Warehouse
Storage
28
Fixed Product Layout (cont.)

• Advantages
• 1. Material movement is reduced.
• 2. Promotes job enlargement by allowing
  individuals or teams to perform the whole job.
• 3. Continuity of operations and responsibility
  results from team.
• 4. Highly flexible can accommodate changes in
  product design, product mix, and product volume.
• 5. Independence of production centers allowing
  scheduling to achieve minimum total production
  time.
• Limitations
• 1. Increased movement of personnel and
  equipment.
• 2. Equipment duplication may occur.
• 3. Higher skill requirements for personnel.
• 4. General supervision required.
• 5. Cumbersome and costly positioning of material
  and machinery.
• 6. Low equipment utilization.

29
Product Layout
30
Product Layout (cont.)

• Advantages
• 1. Since the layout corresponds to the sequence
  of operations, smooth and logical flow lines
  result.
• 2. Since the work from one process is fed
  directly into the next, small in-process
  inventories result.
• 3. Total production time per unit is short.
• 4. Since the machines are located so as to
  minimize distances between consecutive
  operations, material handling is reduced.
• 5. Little skill is usually required by operators
  at the production line hence, training is
  simple, short, and inexpensive.
• 6. Simple production planning control systems
  are possible.
• 7. Less space is occupied by work in transit and
  for temporary storage.
• Limitations
• 1. A breakdown of one machine may lead to a
  complete stoppage of the line that follows that
  machine.
• 2. Since the layout is determined by the
  product, a change in product design may require
  major alternations in the layout.
• 3. The pace of production is determined by the
  slowest machine.
• 4. Supervision is general, rather than
  specialized.
• 5. Comparatively high investment is required, as
  identical machines (a few not fully utilized) are
  sometimes distributed along the line.

31
Process Layout
32
Process Layout (cont.)

• Advantages
• 1. Better utilization of machines can result
  consequently, fewer machines are required.
• 2. A high degree of flexibility exists relative
  to equipment or man power allocation for specific
  tasks.
• 3. Comparatively low investment in machines is
  required.
• 4. The diversity of tasks offers a more
  interesting and satisfying occupation for the
  operator.
• 5. Specialized supervision is possible.
• Limitations
• 1. Since longer flow lines usually exist,
  material handling is more expensive.
• 2. Production planning and control systems are
  more involved.
• 3. Total production time is usually longer.
• 4. Comparatively large amounts of in-process
  inventory result.
• 5. Space and capital are tied up by work in
  process.
• 6. Because of the diversity of the jobs in
  specialized departments, higher grades of skill
  are required.

33
Group Layout
34
Group Layout (cont.)

• Advantages
• 1. Increased machine utilization.
• 2. Team attitude and job enlargement tend to
  occur.
• 3. Compromise between product layout and process
  layout, with associated advantages.
• 4. Supports the use of general purpose
  equipment.
• 5. Shorter travel distances and smoother flow
  lines than for process layout.
• Limitations
• 1. General supervision required.
• 2. Higher skill levels required of employees
  than for product layout.
• 3. Compromise between product layout and process
  layout, with associated limitations.
• 4. Depends on balanced material flow through the
  cell otherwise, buffers and work-in-process
  storage are required.
• 5. Lower machine utilization than for process
  layout.

35
Hybrid Layout

• Combination of the layouts discussed.
• A sample hybrid layout that has characteristics
  of group, process and product layout is shown in
  the following figure.
• A combination of group layout in manufacturing
  cells, product layout in assembly area, and
  process layout in the general machining and
  finishing section is used.

36
Flow Dominance Measure

• Notations
• M number of activities.
• Nij number of different types of items moved
  between activities i and j.
• fijk flow volume between i and j for item k
  (in moves/time period).
• hijk equivalence factor for moving item k with
  respect to other items moved between i and j
  (dimensionless).
• wij equivalent flow volume specified in
  from-to chart (in moves/time period),

37
Flow Dominance Measure (cont.)

• Flow dominance measure f
• where

• f? is the coefficient of variation.
• fL and fU are lower and upper bounds on f?,
  respectively (fL ? f? ? fU).
• The upper bound fU is only guaranteed to work
  when each process plan includes all activities.
  In this case, 0 ? f ? 1.

38
Flow Dominance Measure (cont.)

• Three cases
• 1. f ? 0 ? a few dominant flows exist. ? product
  layout.
• ? can use operations process chart as starting
  point for developing layout and material
  handling system design.
• ? quantitative measures principal source of
  activity relationship.
• 2. f ? 1 ? many nearly equal flows exist.
• ? any layout equally good with respect to flows
  .
• ? qualitative measures principal source of
  activity relationship.
• 3. 0 ltlt f ltlt 1 ? no dominant flows exist. ?
  difficult to develop layout.
• ? process or product family layout .
• ? both quantitative and qualitative measures
  important source of activity
• relationship.

39
Example 2

• Given three machines (activities) labeled 1, 2
  3,

Product A B C
Process Plan 1 - 2 - 3 2 - 1 3 - 1 - 2
Quantities/Shift 10 5 15

• Assume Product B is twice as difficult to move
  as A or C ? hijB 2 and hijA hijC 1

To
1 0 2 ? 5 10 1 ? 15 15
2 1?10 1 ? 15 25 0 0
3 0 1 ? 10 10 0
From
1 2 3
Equivalent Flow Volume From-To Chart
? w12 25, w21 10, etc
40
Example 2 (cont.)
M 3 and
? no dominant flows exist (likely, since 3
different process plans)
41
Qualitative Measures

• Closeness values (A, E, I, O, U, X) used to
  indicate physical proximity requirements between
  activities.
• Relationship Chart can only show symmetric
  relationships, as compared to From-to Chart (wij
  ? wji possible).
• Relationship Chart is starting point for
  developing layout when 0 ltlt f ? 1.
• If f ? 1, then dont need to consider flow (only
  qualitative relationship)
• If f ltlt1, then one can convert equivalent flow
  volumes to closeness values so that material flow
  relationships can be considered along with
  qualitative relationship.
• If f ? 0, then can still convert to relationship
  chart if significant qualitative relationship
  exists, otherwise, just use operations process
  chart.

42
Conversion Method

• To convert equivalent flow volumes to closeness
  values for the example problem, use wij wji to
  make them symmetric.
• Conversion relations
• 20 lt wij wji ? A w12 w21 25 10 ? A
• 12 lt wij wji ? 20 ? E w13 w31 0 15
  ? E
• 5 lt wij wji ? 12 ? I w23 w32 10 0
  ? I
• 0 lt wij wji ? 5 ? O
• wij wji 0 ? U

43
Group Technology

• Group Technology (GT) is a management philosophy
  that attempts to group products with similar
  design or manufacturing characteristics, or both.
• Cellular Manufacturing (CM) is an application of
  GT that involves grouping machines based on the
  parts manufactured by them.
• The main objective of CM is to identify machine
  cells and part families simultaneously, and to
  allocate part families to machine cells in a way
  that minimizes the intercellular movement of
  parts.
• Potential benefits of CM
• Setup time reduction. Improvement in
  quality.
• Work-in-process (WIP) reduction. Improvement
  in material flow.
• Material handling cost reduction.
  Improvement in machine utilization.
• Direct/indirect labor cost reduction.
  Improvement in space utilization.
• Improvement in employee moral.

44
Group Technology (cont.)

• A cellular manufacturing system (CMS) designer
  must consider a number of constraints
• Available capacity of machines in each cell
  cannot be exceeded.
• Safety and technological requirements pertaining
  to the location of equipment and processes must
  be met.
• The size of a cell and the number of cells must
  not exceed a user-specified value.
• Design analysis begins with a machine-part
  indicator matrix A aij of size mn, where m
  is the number of machines and n the number of
  parts. Typically the matrix consists of 0 and 1
  entries
• aij 1 indicates that part j is processed by
  machine i.
• aij 0 indicates that part j is not processed by
  machine i.
• Analysis attempt to rearrange the rows and
  columns of the matrix to get a block diagonal
  form as shown in the following example.

45
Example 3

• Initial Machine Part
• Processing Matrix

• Rearranged Machine-Part
• Processing Matrix

46
Row and Column Masking (RCM) Algorithm

• 1. Draw a horizontal line through the first
  row. Select any 1 entry in the matrix through
  which there is only one line.
• 2. If the entry has a horizontal line, go to
  step 2a. If the entry has a vertical line, go to
  step 2b.
• 2a. Draw a vertical line through the column in
  which this 1 entry appears. Go to step 3.
• 2b. Draw a horizontal line through the row in
  which this 1 entry appears. Go to step 3.
• 3. If there is any 1 entries with only one line
  through them, select any one and go to step 2.
  Repeat until there are no such entries left.
  Identify the corresponding machine cell and part
  family. Go to step 4.
• 4. Select any row through which there is no
  line. If there are no such rows, stop. Otherwise,
  draw a horizontal line through this row, select
  any 1 entry in the matrix through which there is
  only one line, and go to step 2.

47
Example 3 Solution

• Identification of the First Machine
• Cell and Part Family

• Identification of the Second Machine
• Cell and Part Family

48
Single Linkage (S-Link) Clustering Algorithm

• S-Link is the simplest of all clustering
  algorithms based on the similarity coefficient
  method.
• The similarity coefficient between two machines
  is defined as the number of parts visiting the
  two machines divided by the number of parts
  visiting either of the two machines.
• 1. pairwise similarity coefficients between
  machines are calculated and stored in the
  similarity matrix.
• 2. The two most similar machines join to form
  the first machine cell.
• 3. The threshold value (the similarity level at
  which two or more machine cells join together) is
  lowered in predetermined steps and all
  machine/machine cells with the similarity
  coefficient greater than the threshold value are
  grouped into larger cells.
• 4. Step 3 is repeated until all machines are
  grouped into a single machine cell.

49
Example 4 Initial Machine Part Matrix
50
Example 4 Initial Similarity Coefficient Matrix
Machine
M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
0.08 0.00 0.43 1.00
0.08 0.00 0.80 0.00 0.00 0.80
0.00 0.80 0.50 0.00 0.00 0.00 0.00
0.10 0.00 0.00 0.00 0.00 0.25 0.50
0.00 0.00 0.27 0.45 0.00 0.00 0.00
0.00 0.00 0.00 0.83 0.36 0.43 0.45 0.23
0.43 0.43 0.36 0.00 0.17 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.57 0.37 0.67 0.00
Machine
51
Example 4 Dendrogram Based on S-Link
Similarity Levels
52
Example 4 Machine Part Groups using S-Link
53
Average Linkage (A-Link) Clustering Algorithm

• The similarity coefficient between two machine
  cells is defined as the average of pairwise
  similarity coefficients between all members of
  the two cells.
• 1. Compute pairwise similarity coefficients
  between machines and construct the similarity
  coefficient matrix.
• 2. Merge the two most similar machines into a
  single machine cell.
• 3. Compute the similarity coefficients between
  the newly formed machine cell and the remaining
  cells. Revise the similarity coefficient matrix.
• 4. The threshold value (the similarity level at
  which two or more machine cells join together) is
  lowered in predetermined steps and all
  machine/machine cells with the similarity
  coefficient greater than the threshold value are
  grouped into larger cells. Repeat steps 3 and 4
  until all machines are grouped into a single
  machine cell.

54
Example 4 Revised Similarity Coefficient Matrix I
Machine Cell
(M1, M4) (M2, M6) M3 M5 (M7, M9) M8 M10
M11
(M1, M4) (M2, M6) M3 M5 (M7, M9)
M8 M10 M11
0.04 0.00 0.47
0.80 0.00 0.00 0.00 0.00 0.05
0.00 0.00 0.26 0.50 0.00 0.41
0.43 0.41 0.23 0.43 0.00 0.17
0.00 0.00 0.00 0.00 0.62 0.36 0.00
Machine Cell
55
Example 4 Revised Similarity Coefficient Matrix
II
Machine Cell
(M1, M4 , M5) (M2, M6) M3 (M7, M9, M11) M8
M10
(M1, M4, M5) (M2, M6) M3 (M7, M9,
M11) M8 M10
0.02 0.00 0.47
0.00 0.00 0.03
0.00 0.26 0.50 0.39 0.43
0.41 0.23 0.00 0.17
Machine Cell
56
Example 4 Revised Similarity Coefficient
Matrices III IV
57
Example 4 Dendrogram Based on A-Link
Similarity Levels
58
Example 4 Machine Part Groups using A-Link
59
Comparison

• RCM is the simplest clustering algorithm.
• A major disadvantage of RCM is that when the
  machine part matrix contains one or more
  bottleneck machines (machines that belong to more
  than one cell) or exceptional parts (parts that
  are processed in more than one cell), the
  algorithm may provide a solution with all
  machines in a cell and all parts in a
  corresponding part family.
• The major advantages of S-Link are its simplicity
  and minimal computational requirement. In S-Link,
  once pairwise similarity coefficients are
  computed and the similarity coefficient matrix is
  constructed, the matrix can be used to develop
  the dendrogram which represents the machine cells
  at different threshold values.
• The major drawback of S-Link is the chaining
  problem. Due to the chaining problem, two machine
  cells may join together just because two of their
  members are similar while the remaining members
  may remain far apart in terms of similarity.
• The chaining problem of S-Link can be overcome by
  using A-Link. Since in A-Link two machine cells
  merge based on the overall similarity coefficient
  between all their members, it is unlikely that
  two similar members in two cells cause the cells
  to merge while other members are not similar
  enough. A-Link provides a more reliable solution
  to the machine cells formation problem.